Referring now to FIG. 1, a data link layer 10 of the open systems interconnection (OSI) model includes a logical link control (LLC) layer 12 and a media access control (MAC) layer 14. The LLC layer 12 addresses and exchanges data with a network layer 16. The MAC layer 14 provides an interface between the LLC layer 12 and a physical layer 18.
The MAC layer 14 frames data for transmission over the network and then passes the frame to the physical layer 18 for transmission as a stream of bits. In other words, the MAC layer 14 frames data into distinct units or packets that are transmitted one at a time over the network.
The physical layer 18 typically includes a physical coding sublayer (PCS) 20, a physical medium attachment (PMA) sublayer 22, and an autonegotiation sublayer 24. A medium dependent interface (MDI) 26 such as an RJ-45 connector connects the physical layer 18 to media 28 such as twisted pair wires, optical fiber or other media. The IEEE 802.3 specification, which is hereby incorporated by reference, further defines how physical network interfaces operate with different types of media such as coaxial cable, twisted-pair cable and optical fiber.
To improve flexibility, the physical layer 18 of some network devices has been designed to be connected to different types of media. The manufacturer and/or the user may not know the type of media that will be used at the time of manufacturing or purchase. The type of media that is used may also change over time.
For example, the physical layer 18 is selectively connectable to copper or optical fiber. Currently, the PCS sublayer 20 of the physical layer 18 is programmed to handle the specific type of media that will be used. For example when optical fiber is used, the operating mode of the PCS 20 is programmed to provide an optical interface. If the user later decides to use a different type of media such as copper, the operating mode of the PCS 20 is programmed to provide a copper interface. The reprogramming process increases the cost of operating the network.
The autonegotiation sublayer 24 initiates the exchange of information between two connected network devices and automatically configures the devices to take maximum advantage of their respective abilities. The autonegotiation sublayer 24 advertises the abilities of the network device, acknowledges receipt, identifies common modes of operation, and rejects the use of operational modes that are not shared or supported by both devices. When more than one common mode of operation exists between the devices, an arbitration function of the autonegotiation layer 24 identifies and selects a single mode of operation. After autonegotiation is complete, the devices establish a link and exchange data.